The present disclosure generally relates to scintillation materials used to detect radiation such as, but not limited to, X-rays, gamma rays (γ-rays), and thermal neutron radiation.
A scintillator is a material that can absorb high-energy particles and convert these particles to multiple low-energy photons. Scintillation materials are scientifically and economically significant in conjunction with photodetectors to detect high-energy photons, electrons, and other particles in various applications, which include medical imaging, geological exploration, homeland security, and high-energy physics. In order to maximize the values of the scintillator in these applications, characteristics including high scintillation light yield, fast scintillation decay time and rise time, good energy resolution, high degree of proportionality, proper emission wavelength, and good thermal response over a wide temperature range are desired.
Halide scintillators, which contain a monovalent or a divalent external activator, have been shown to be a promising class of scintillators. Monovalent external activators include Tl+, Na+, and In+. For example, CsBaI5 doped with Tl+, Na+, and In+ scintillators are manufactured and used as γ-ray detectors in “Scintillation Properties of CsBaI5 Activated with Monovalent Ions Tl+, Na+ and In+,” by M. Gascon, et al., Journal of Luminescence, 2014, 156, 63-68. Divalent external activators include Eu2+ and Yb2+. Several Eu2+-doped halide scintillators showing a high light output and melting congruently, which allows the scintillators to be grown using the Bridgman-Stockbarger technique, have been described. For example, Eu2+-doped CsSrI3 scintillators are prepared and their photophysical properties are disclosed in “Crystal Growth and Characterization of CsSr1-xEuxI3 High Light Yield Scintillators,” by K. Yang, et al., Rapid Research Letters, 2011, 5, 43-45 and in “Optical and Scintillation Properties of Single Crystal CsSr1-xEuxI3,” by K. Yang, et al., Nuclear Science Symposium Conference Record (NSS/MIC), 2010, 1603-1606. U.S. Patent Application Publication No. 2012/0273726 by M. Zhuravleva, et al. reported the scintillation properties of CsSrBr3 doped with Eu2+. Another example, “New Single Crystal Scintillators, CsCaCl3:Eu and CsCaI3:Eu,” by M. Zhuravleva, et al., Journal of Crystal Growth, 2012, 352, 115-119, described the scintillation properties of CsCaCl3 and CsCaI3 doped with Eu2+. Scintillator crystals of CsBaI3 doped with Eu2+ were found to have excellent scintillator properties as disclosed in “New Promising Scintillators for Gamma-Ray Spectroscopy: Cs(Ba,Sr)(Br,I)3,” by U. Shirwadkar, et al., IEEE Nuclear Science Symposium Conference Record, 2011, 1583-1585. International Application Publication No. WO 2015/010055 by L. Stand, et al. described the scintillation properties of doped (e.g., europium-doped) ternary metal halides having general formulas A2BX4 and AB2X5, where A is an alkali metal, B is an alkaline earth metal, and X is a halide.
The use of mixed-halide scintillators, i.e., scintillators containing two or more different halide atoms, has been proposed as a means of increasing scintillator light output as shown in “Scintillation Efficiency Improvement by Mixed Crystal Use,” by A. V. Gektin, et al., IEEE Transactions on Nuclear Science, 2014, 61, 262-270. For example, mixed-halide elpasolite scintillators of Cs2NaYBr3I3 and Cs2NaLaBr3I3 doped with the trivalent activator Ce3+ are fabricated and their optical properties reported in “Two New Cerium-Doped Mixed-Anion Elpasolite Scintillators: Cs2NaYBr3I3 and Cs2NaLaBr3I3,” by H. Wei, et al., Optical Materials, 2014, 38, 154-160. Ce3+-based single crystal mixed-halide scintillators are reported in “The Scintillation Properties of CeBr3-xCix Single Crystals,” by H. Wei, et al., Journal of Luminescence, 2014, 156, 175-179. In another example, in “Scintillation and Optical Properties of BaBrI:Eu2+ and CsBa2I5:Eu2+,” IEEE Transactions on Nuclear Science, 2011, 58, 3403-3410, G. Bizarri, et al. reported Eu2+-doped scintillators of BaBrI. International Application Publication No. WO 2015/172026 by L. Stand, et al. described the scintillation properties mixed-halide scintillation materials having general formulas AB(1-y)MyX′wX″(3-w) and A(1-y)BMyX′wX″(3-x), where 0≤y≤1, 0.05≤w≤1, A is an alkali metal, B is an alkaline earth metal, X′ and X″ are two different halogen atoms, and M is a divalent external activator in the former formula and a monovalent external activator in the latter formula.